Please note that what you ask is already answered in each and every of our release announcements of the past few months. Please do read our release announcements. I actually put some very useful and important information in them ;) Anyway, here we go.
Joomla! 1.5 users will still be supported for using Akeeba Backup 3.4.3 on their sites until August 2012. After that point, the Joomla! project itself will completely stop supporting Joomla! 1.5. This means that Joomla! 1.5 will become vulnerable, end-of-life software which should not be used on live sites. The Joomla! project has announced its plans for Joomla! 1.5's end-of-life back in January 2011 when Joomla! 1.6 was released.
Similarly, we have ceased support for Joomla! 1.6 since September 2011 and ceased support for Joomla! 1.7 since March 2012, that is as soon as these platforms were deemed end-of-life. Also note that Joomla! 1.5.0-1.5.25, 1.6.x and 1.7.x all have very grave security vulnerabilities. There are instructions out there which allow any monkey with a computer to hack sites based on those ancient Joomla! releases in 5 minutes or less. If you still have a live site with a vulnerable version of Joomla!, upgrade as soon as possible. If you want to continue using a vulnerable version of Joomla! at your own risk you may use one of the unsupported versions of our components mentioned in our version compatibility page: https://www.akeebabackup.com/compatibility.html
Side note: Joomla! 1.5 is no longer the most used Joomla! version, at least among Akeeba Backup users. The vast majority of our support tickets over the last two months and a half have been about Joomla! 2.5 sites. Prior to Joomla! 2.5's release, about 60% of the tickets were about Joomla! 1.5. This means that everyone is scrambling to upgrade their sites. One more reason not to let Akeeba Backup fall behind to satisfy the ever-shrinking minority of users who are still using Joomla! 1.5.
Regarding the update emails, please note that I do not send out version update emails for the simple reason that I do not know your domain name, email address and installed Akeeba Backup version. I also vehemently disagree with having a mailing list to send out version update emails – I believe the RSS feed of our frontpage is much better in that respect. The emails are sent out by a plugin installed in your site. Just disable the "System - Akeeba Backup Update Check" plugin and the emails will, of course, stop.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!